Scotty,
Assuming you have the standard MAC trim servo, it should stop at the
travel limits.  Something isn't right with your servo or installation.
I would suggest you open up the servo and take a look.  You'll be able
to see the limit switches.  Also, a 'flimsy' trim tab can lead to
flutter as it is not a mass balanced surface.  The tab should be rigid
in all positions.
Good luck.
Chris Zavatson
N91CZ
360 std